The present invention pertains to electrical igniters and more particularly to electrical igniters for regenerative liquid propellant guns.
The basic function of the igniter in a regenerative liquid propellant gun is to generate hot gas and discharge it into the gun combustion chamber. The igniter has to provide enough pressure and temperature in the combustion chamber to start the regenerative combustion process in the gun.
Despite recent progress toward a practical large caliber regenerative liquid propellant gun, igniter development for the gun is still in its infancy. Only solid propellant gas generators have been used effectively as igniters for the regenerative liquid propellant gun in small and medium caliber guns and are expected to perform as well in large calibers. Various igniter concepts, which are not based on solid propellants, have been suggested but none seems practical. From the logistical point of view, the ideal igniter would be based solely on the liquid gun propellant itself. However, considering the requirements for an igniter, the development of such an igniter is not an easy task. An igniter has to provide about 18 MPA pressure in the combustion chamber of the gun in about 5 milliseconds. for a large caliber gun, such as a having a 5000 cubic centimeter combustion chamber, a liquid gun propellant charge in excess of 100 grams is required.
Two basic approaches for combusting a large mass of liquid gun propellant in a short duration are plausible. In a first approach, the liquid gun propellant is ignited to combust in a bulk loaded external chamber. A vent can then be opened to discharge the gas into the combustion chamber of the gun. In the second approach, the liquid gun propellant is introduced directly into the gun chamber and is ignited there. Both approaches have drawbacks and neither has been successfully proven.
Concerning the ignition of the liquid gun propellant, it is rather straightforward in the first approach. Electrical ignition of bulk loaded liquid gun propellants have long been demonstrated. It is best accomplished by arc discharge and involves energy deposition of tens of joules which can readily be achieved. However, controlling the combustion, and the timely venting of the hot gas, strain the practicality of the approach. The risk is that the combustion may proceed too rapidly to extreme pressures resulting in the mechanical failure of the igniter. An operation with an externally loaded igniter has been recently demonstrated but it involved only 2 cubic centimeters of liquid gun propellant, LGP 1846, and a 1.6 millimeter vent orifice permanently open. Such an igniter is not practical for two reasons. First, since the liquid gun propellant is not sealed, it can leak prior to firing; and, second, large practical masses of liquid gun propellant would require much larger vents. Successful ignition to a complete combustion of bulk loaded liquid gun propellant having a large permanent vent is very difficult to achieve with reasonable electrical energy.
The second approach does not require operation at very high pressures but its practicality is also questionable. A large mass of liquid gun propellant has to be injected rapidly into the gun chamber in the form of a fine spray. This is essential, since the atmospheric pressure ignition of low loading density liquid gun propellant is very difficult. Only a fine uniformly distributed spray may be ignited, possibly by a stream of hot gas. The prompt atomization of the liquid gun propellant in the low density chamber gas environment can be practically obtained by blasting the liquid gun propellant with high velocity gas which, if hot, would also serve to ignite the liquid gun propellant. Thus, the second approach is based on the availability of auxiliary high pressure and temperature gas, which is an undesirable system complication.